Angular velocity sensors are often used in navigation systems or other applications, and downsizing thereof is requested. Therefore, in recent years, the structure of proposed sensors has been changing from one using bulk piezoelectric material, e.g. quartz crystal, to one using piezoelectric thin film, e.g. lead zirconate titanate (PZT). This is because piezoelectric thin film, such as PZT, has a piezoelectric constant extremely larger than that of bulk piezoelectric material, such as quartz crystal, and thus is downsized more easily.
Although the use of piezoelectric thin film can downsize an angular velocity sensor, there is a problem in production to be solved, which is never posed by bulk piezoelectric material. Because piezoelectric thin film is much thinner than bulk piezoelectric material, the electrodes sandwiching both surfaces of a piezoelectric thin film are prone to short-circuiting. Specifically, in the outer peripheral area of the piezoelectric thin film, the electrodes on both surfaces are prone to short-circuiting. It is necessary to ensure prevention of the short circuits in such an area.
The Japanese Patent Unexamined Publication No. H09-331087 discloses a structure in which a piezoelectric thin film is formed over a lower electrode layer in order to improve adherence in directly forming the piezoelectric thin film on a substrate. This example does not include the description about prevention of short circuits between the lower and upper electrode layers. However, this structure can prevent the short circuits.
The Japanese Patent Unexamined Publication No. 2001-113710 aims to realize a uniform shape to reduce variations in the displacement of a piezoelectric element. It discloses that appropriately setting the conditions for dry etching or wet etching allows the edges of a piezoelectric thin film to be etched into a taper shape.